Hard disk technology is constantly evolving. Advances in nanomagnetics, magnetic ultrathin films, magnetoelectronics, as well as device processing, have advanced this technology. It can be expected that the future will continue to bring further advances in hard disk technology.
The recording head of a hard disk has three main components: (1) the read sensor (“reader”); (2) the write transducer (“writer”), which is a microfabricated planar electromagnet with a narrow pole that creates a high density of magnetic flux in proximity to the media; and (3) the slider, which is a shaped piece of substrate (typically alumina-titanium carbide) onto which the writer and read sensor are built, and is engineered to “fly” only a few nanometers above the spinning media disk.
The writer is designed to fly just a few nanometers above a spinning disk at up to 15000 revolutions per minute.
The subject of the present invention is the writer, but it is understood that for any writer, there is an appropriate combination of sensor and slider which forms a coherent recording head device and, together with the chosen media, mechanical characteristics, and electronics, forms a complete recording system. The recording environment in which the head is expected to operate is first introduced, including media characteristics, magnetic interference and shielding, and signal-to-noise (SNR) considerations. These constraints put specific boundaries on the sizes, geometries, and magnetic properties which a writer must achieve.
The magnetic recording process utilizes a thin film transducer for the creation or writing of magnetized regions (bits) onto a thin film disk and for the detection or reading of the presence of transitions between the written bits. The thin film transducer is referred to as a thin film head. It consists of a read element, which detects the magnetic bits, and a write element, which creates or erases the bits.
In order to meet the ever increasing demand for improved data rate and data capacity, research has focused on the development of perpendicular recording systems. A traditional longitudinal recording system stores data as magnetic bits oriented longitudinally along a track in the plane of the surface of the magnetic disk. This longitudinal data bit is recorded by a fringing field that forms between a pair of magnetic poles separated by a write gap.
A perpendicular recording system, on the other hand, records data as magnetic transitions oriented perpendicular to the plane of the magnetic disk. FIG. 1 is a schematic of the recording process in a perpendicular recording system. Shown in FIG. 1 is read sensor 102, write element 104, and recording medium 106. The perpendicular write element 104 has a write pole with a very small cross section and a return pole having a much larger cross section. A strong, highly concentrated magnetic field emits from write pole 114 in a direction perpendicular to recording medium 106 to magnetize perpendicular bits 108. Perpendicular write element 104 writes magnetic transitions vertically within recording medium 106 by orienting the magnetic field 116 perpendicular to the direction of recording medium 106. Magnetic field 116 created by this perpendicular head returns through a magnetically soft underlayer 110 within the medium. In this way the recording medium 106 lies within the write gap.
The resulting magnetic flux returns through return pole 112 where it is sufficiently spread out and weak that it will not erase the signal recorded by write element 104. The resulting perpendicular write fields 116 can be up to two times larger than longitudinal write fields, thus enabling the perpendicular write element to write information on high coercivity media that is inherently more thermally stable. In perpendicular recording, the bits do not directly oppose each other resulting in a significantly reduced transition packing. This allows bits to be more closely packed with sharper transition signals, facilitating easier bit detection and error correction. During a read operation, read sensor 102 detects perpendicular bits 108 on recording medium 106.
In a disk recording system, successive bits are written onto the disk surface in concentric rings or tracks separated by a guard band. The head transducer is attached to a suspension, and the suspension is attached to an actuator which controls the position of the transducer in a plane above the disk surface. A specially-designed topography on the lower surface of the slider (known as the air bearing surface or ABS) allows the head to “fly” above the rotating disk (typically 4200-15000 rpm), and controls the height of the transducer above the disk surface, typically 10 to 15 nm.
Referring now to FIG. 2, there is shown an implementation of a disk drive 200. As shown in FIG. 2, at least one rotatable magnetic disk 212 is supported on a spindle 214 and rotated by a disk drive motor 218. The magnetic recording on each disk is in the form of annular patterns of concentric data tracks on the magnetic disk 212.
At least one slider 213 is positioned near the magnetic disk 212, each slider 213 supporting one or more magnetic head assemblies 221. As the magnetic disk rotates, slider 213 moves radially in and out over the disk surface 222 so that the magnetic head assembly 221 may access different tracks of the magnetic disk where desired data are written. Each slider 213 is attached to an actuator arm 219 by way of a suspension 215.
Suspension 215 provides a spring force which biases slider 213 against disk surface 222. Each actuator arm 219 is attached to actuator 227. Actuator 227 as shown in FIG. 2 may be a voice coil motor (VCM). The VCM comprises a coil movable within a fixed magnetic field, the direction and speed of the coil movements being controlled by the motor current signals supplied by controller 229.
During operation of the disk storage system, the rotation of magnetic disk 212 generates an air bearing between slider 213 and the disk surface 222 which exerts an upward force or lift on the slider. The air bearing thus counterbalances the spring force of suspension 215 and supports slider 213 off and slightly above the disk surface by a small, substantially constant spacing during normal operation.
The various components of the disk storage system are controlled in operation by control signals generated by control unit 229. Control signals may also include internal clock signals. Typically, control unit 229 comprises logic control circuits, digital storage and a microprocessor. Control unit 229 generates control signals to control various system operations such as drive motor control signals on line 223 and head position and seek control signals on line 228. The control signals on line 228 provide the desired current profiles to optimally move and position slider 213 to the desired data track on disk 212. Write and read signals are communicated to and from write and read heads 221 by way of recording channel 225.
With reference to FIG. 3, the orientation of magnetic head 221 in slider 213 can be seen in more detail. FIG. 3 is an ABS view of slider 213, and as can be seen, the magnetic head, including an inductive write head and a read sensor, is located at a trailing edge of the slider.
In perpendicular magnetic recording, the write head may include a trailing shield (TS) of magnetically permeable material that faces the recording layer and is spaced from the write pole in the along-the-track direction by a nonmagnetic gap. The TS slightly alters the angle of the write field and makes writing more efficient.
The write head may also include a pair of side shields located on opposite sides of the write pole in the cross-track direction and separated from the write pole by a nonmagnetic gap layer. The side shields control the write width and help reduce adjacent-track-erasure. Typically the TS and side shields are connected or formed as a single-piece structure to form a wraparound shield (WAS) that generally surrounds the write pole. A perpendicular magnetic recording write head with a WAS is described in U.S. Pat. No. 7,002,775 B2, assigned to the same assignee as this application.
Perpendicular magnetic recording at high a real density is limited by the strength of the write field and the write field gradient at the point of writing. Additionally, a high write field increases the likelihood of erasure of adjacent tracks, especially when the write head is located at a high skew angle relative to the data track to be written.
The above description of a typical magnetic disk storage system, and the accompanying illustrations of FIG. 1-3 are for representation purposes only. It should be apparent that disk storage systems may contain a large number of disks and actuators, and each actuator may support a number of sliders.
What is needed is a well-controlled process for making a magnetic recording write head. With the improved process, the magnetic recording write head can be made to exhibit better performance.